Method of manufacturing a



INVENTORS Harry Bender Wlll M nflw rws ATTORNEYS mm B. Voorhis 2SHEETS-SHEET 1 Fig H BENDER ET AL METHOD OF MANUFACTURING A FILAMENTUNIT Sept. 9, 1952 Original Filed Aug. 4, 1945 P 9, 1952 H. BENDER ET ALMETHOD OF MANUFACTURING A FILAMENT UNIT 2 SHEETS-SHEET 2 Original FiledAug. 4, 1945 INVENTORS Hurry Bender William B. Voorhis ATTORNEYS Fig.lO

Patented Sept. 9, 1952 Harry Bender, Princeton, and William B. Voorhis,East Orange, N. J assignors to Tung-Sol Lamp Works, Inc., Newark, N. J acorporation of Delaware Original application August 4, 1945, Serial No.

608,960, now Patent No. 2,482,826, dated September 27, 1949. Divided andthis application October 30, 1948, Serial No. 57,482

This invention relates to thermionic tubes and particularly to heatingfilaments and mounts therefor, although certain features oftheinvention'have other applications.- 1

Heating filaments and mounts-in cathode assemblies of the conventionalpractice are not entirely satisfactory and particularly assemblies Oneobject of the invention is a filament mounting structure and cathodeassembly whereby -the above difficulties and others are minimized oravoided.

A further object of the invention is aheating filament and cathodeassembly of the above indicated character which is characterized by thefirm and stable support of the elongated coil-filament inside thecathode against collapse and by the ease of welding the filamentterminals to the lead wires to form both a firm support and electricalconnection and by the ease of forming the filament and assembling it tothe mount.

A further object of the invention is a coiled filamentary element of theabove indicated character having a novel and improved end connector orterminal and support.

A further object of the invention is a novel and improved method ofmaking heating filament units for thermionic tubes and particularlyelongated high voltage filaments which is characterized by markedeconomy'in the use of raw materials, by a substantial reduction in thenumber of manufacturing steps or operations, by the ready adaptabilityofthe method to the making of filamentary units embodying filaments of thefineness required for high voltage heaters and by a substantial.decrease in material loss.

Further objects of the invention will hereinafter appear.

For a better understanding of the invention reference may be had to theaccompanying drawings forming a part of this application, wherein Fig. 1is a side view ofa therminoic tube embodying the invention;

Fig. 2 is a side view on an enlarged scale of a filament mount andcathode assembly embodying the invention;

2 Claims. (Cl. 29-2518) Fig. 3 is a sun further enlarged view of a partof the mount shown in Fig. 2;

' Fig. 4 is a view similar to Fig.3 but disposed at right anglesthereto; I

Figs. 5 and 6 are sectional views along the lines 5-5 and 6-6 of Fig.3;.

Fig. '7 is a view similar to Fig. 3 showing a modification; Y

Fig. Bis a diagrammatic view'illustrating steps in making of thefilamentary units according to the invention; and Y v Figs. 9 and 10illustrate further steps in the method of manufacture.

The invention is illustrated as embodied in a thermionic tube I havingtwo cathode elements, only one being shown and this one being indicatedat'2 and being suitably mounted between the upper and lower insulatingplates 3 and 4. This cathode 2 is hollow and of conventional make. It

may be circular in cross sectionor of other conventional section. In theembodiment illustrated the cathode element 2 is tubular and circular Iin cross section. The filament element of the of the insulatingmaterials used for that purpose so as to prevent short-circuiting ofadjacent coilsv or the short-circuiting of any part of the filament bycoming in contact with the interior surface of the metallic cathode 2.At I are shown the lead or support wires extending from the press of thetube with their ends I turned over at an angle and fastened to the endstructure '6 of the filament 5 as, for example, by welding.

In Figs. 3, 4, 5 and 6 are illustrated thesupporting end structures. orterminals of the coiled filament-.5. Each of the terminalsv B isprovided with'a cylindrical supporting part 8 which is of substantiallythe same diameter as the diameter of the coil into which the filament 5is formed with that part of the filament 5 being closely wound about thesupport 8 with the turns of the coil 5' engaging the surface of thecylindrical support 8. This support 8 is of a shape conforming to thecoils of the filament 5 and as indicated since the coils are circularthe support 8 is circular. The end structure or terminal 6 also embodiesanother filament supporting part 9 which is formed integrally with thesupporting part 8 and this part 9 of the terminal is'fastened as bywelding to the lead wire arm 1'. This part 9 of the filament terminal isflattened on one side and the portion of the turns of the filament coil5' are embedded in the flattened side of the part 9. In the particularembodiment shown the part 9 is flattened on opposite sides to form flatsurfaces IE! between which are dis-' posed round surfaces H and'Figs. iand 5 show the opposite portions of the turns of the coils 5 as embeddedin the flattened sides 19 of the terminal supporting part 9. The turnsof the coils 5 pass around the unfiattened edges H of the supportingpart 9 without being embedded therein but these portions of the turnspress closely against the rounded edges i I as the turns of the coils 5'closely surround the terminal supporting part 8. By embedding the finefilamentary wire of the filament terminal in the terminal supportingpart 9 the filament ends arev thereby firmly anchored to the terminalsupporting part 51 a ainst unravelling or dislodgment and the flattenedside or sides'lfl where the filament is embedded afford a line contactwith the lead arm 7' for-firmly welding the terminals to the lead wires.

As illustrated in Fig. 3 the filament unit and the cathode 2 arepreferably assembled with the fila- .ment terminal supports extending upinto the cathode a short distance as. for example, a distance of from 1to 2 millimeters.

)The filamentary unit and cathode assembly have the advantages, amongothers, of having F a rigid terminal supporting and welding part 9 withthe filament turns embedded therein s as v to. prevent any tendency ofthe filament to become dislodged or removed from the support, and

. so as to present a. solid piece of metal 9 to the lead arm 7' to whichit is to be welded and of ,having an adjacent and integral supportingter- .minal part 8 about which the filament turns are closely woundwithout-being embedded therein to ;form a. sort of cushioning sectionfor the heating'or body part 5 of the filament. The support- I ing andmounting terminal part 6 of thefilamentend may be of any suitable lengthbut we 'have obtained satisfactory results where this part is around 8to .9 millimeters and the structure and assembly described render easierand facilitate the mounting of. the filament units on the lead wires,and the assembly in the cathode tubes 2, l the filament terminal forminga rigid integral aligning support for the filament during this mountingand assembly operation. Another advantage of this filament unit is thatthere is no appreciable tendency for coating material with which thefilament body 5 are treated to seep along the terminal 6 to the weldingpart '9 and there to interfere with the welding and the I the terminalsupporting and mounting part 6 is provided with a slightly elongatedreduced in diameter portion .or tapered end 8{ and with this structure asubstantially reduced tube loss is v obtained as compared with theconventional practice. It is believed that, this reduction in tube lossis due in part to the seepage of coating material on the under sides ofthe coils of the filament 5 adjacent and along the tapered portion 8which tends-to strengthen the coatings applied to the part of the coil 5in that region where the filament 5 tends to form bends and in 4 part tothe tendency to form a more gradual bend at the tapered or reduced endbut we do not desire to be, restricted to any theory of functioning inthis respect.

The method of manufacturing the filament elements 5, 6 isdiagrammatically illustrated in Figs. 8 to 10. A filamentary wire [5 isclosely coiled and wound about a metallic wire core Hi from a wirecarrying reel l1 somewhat in the conventional manner of forming coilfilaments of less fine wire. This step is illustrated at A, Fig. 8. Withthe filamentary wire it thus wound in closely formed coils and closelyabout the surface of the wire core or mandrel [6 suitable lengths ofthis combined filamentary coil and core wire [6 are severed as indicatedat B in Fig. 8. The terminal supports for the filamentary part of thefilament are formed out of the core or mandrel wire I6 and before orafter the severing of the lengths l3, either at one or both Q Qsimultaneously, the ends of the lengths-itfcrmed or to be formed areflattened and the filamentary wires are embedded in the fiatsides f themandrel thus flattened toform the fiat sided welding parts 9 of theterminals. This may be done on any suitablehand or machine press,omittedfor convenience in illustration. In the particular embodimentshown, the lengths I8 are severed at both ends and then flattened andthe wires embedded. i

With the ends of the lengths [8 thus flattened, with the filamentarywire l5 at'the ends of the lengths embedded in the fiat sideso'f thefiat portion 9 the lengths 18 are subjected to a suitable acid bath todissolve out the mandrel '16 within the main heating portion 5'ofthefilament, and the supporting and reinforcing terminals 6 above describedare at the sametime formed. In -the particular embodiment shown thefilament portion 5 as described above is formed into two substantiallyparallel branches with the terminals ii welded to the adjacent'l'eadwire supporting arms '5' as desi'zriloed" above, and the next step D ofFig. 8 is the formation of the lengths is into a V 18. With the lengthsit thus formed the legs of the V are subjected to a suitable acid bathto dissolve' out the core wire it, leaving the heatmg'filament portion 5without any core, but leaving a flatagrammatically in Fig. 9 byproviding any suitable support 20 for a multiple number of the lengthsIS with the support or supports 26 engaging or gripping the flattenedends 9 of the lengths. With the lengths Iii thus supported the supportor supports 20 are lowered into an acid bath 2! and the legs of the Vlengths 16' are maintainedin the bath 2| until the mandrel it of thelegs of thevs is completely dissolved out except for the ends 6 abovedescribed consisting'of the flattened parts 9 and the part8.

If it is desired tr.) reduce the diameter of the inner ends of the parts8 of the terminal$ -,to form the reduced diameter part 3201? Fig. 7, thesupports or carriers 20 are first lowered to a depth sufficient to formthe terminal. portions 6 of the desired length by whollydissolvin'g outthe intermediate partof thecore wireldq The supports or carriers 20 arethen lowered slightly,

' as indicated in dotted lines. in Fig. ,9, vto dissolve off a part ofthe periphery of the inner ends of j the terminal portions 8 thereof toform an inner supporting part or parts at the; extreme end of theportions ii,- which parts are of substantially. lessdiameter than thediameter of the, coils of the filament 5. We have roughly indicated inFig. '7 the generally tapered shape of such extreme end portions 8'which preferably extend in the mounted position a short distance intothe lower nd of the cathode 2, as shownin Fig. 7. f -With the'supportingterminals 6 thus formed,

" maybe of any suitable character so long as the portions intermediatethe terminals 6 may be readily dissolved without at the "same timeimparing the filam'entary coil. Itm'ay for example be of brass, iron, ormolybdenum. The particular 'acid' bath depends on the 'characterof theman-- fldre'l "or core Is and when-molybdenum is useda bath of nitricand sulfuric acid may be used to dissolve it'out. In dissolving the coreor mandrel asillustrated in Fig. '9, the level of the'bath should bekept fixed so that with a fixed support coating material of theconventional practice to I insulate the coils of the filament from eachother and against short circuiting contact with the cathode 2 againstthe interior of which the filament branches or legs rest for support.This may be effected by utilizing the same holder or supports 28 fordipping the V filaments in a cataphoretic bath for coating andaccordingly after that portion of the mandrel or core 16 between theterminal supports 6 is dissolved, the holder and the filament arewithdrawn and washed and the filaments dipped in the cataphoretic bath,as shown in Fig. 10, the bath being diagrammatically indicated at 22.

The filament units thus completed, the filaments are ready for mountingupon the lead wires 1,1 and assembly into the cathode 2. The tendency ofthe insulating coating material to seep along the filament terminals andthere interfere with the forming of a secure weld and electricalconnection with the leads I, 1' is minimized or entirely avoided byreason of the particular structure of the supporting terminals 5 whereinthe filamentary wire coils are bound about or closely formed about theperiphery of the supports with no free spaces on the interior of thecoil at the terminals to induce such seepage. Where the terminals 6 areprovided with the ends 8 of reduced diameter as compared with the innerdiameter of the filamentary coils, the coating material seeps along theturns of the coils about the reduced portion 8' to form a reinforcementof the coating against chipping at this point where the sharper bends ofthe nonself-supporting filament are likely to occur and in the coatingstep the filament may be dipped to a point above the tip of the reducedportion 8' of the support, or to a depth co-extensive with the length ofthis reduced portion 8'. The fiattened and filament embedded ends 9 ofthe filament units prevent any tendency of the filament coils to ravel,creep or become dislodged, and also forms easily weldable ends forwelding to the lead wires 1, 1 while the turns of the closely woundfilament about the portions 8 form cushioning means between the portionsof the filaments embedded and rigidly fastened to the parts 9 on the onehand, and the heating or body part 5 of the filament. The part 8 alsoperforms an alining function for assisting the operator in assembly withthe cathode 2 while the reduced diameter or tapered part 8 of thesupport imparts the advantages above set forth.

The filament lengths or forms I8 may be cleaned in any conventionalmanner before dissolving the mandrel or core I'E out of the lengths as,for example, by subjecting them to caustic or some other conventionalcleaning means. After such cleaning the filament lengths or forms I8 maybe fired at high temperature to set the filament coils as, for example,in a hydrogen atmosphere furnace. The core or mandrel wire 16 or holder211 only the part of the mandr'e'l or core 1 between the terminalsupports '6is' affected and while the temperature of the dissolving bathmay vary with different materials of mandrels or cores, with; amolybdenum mandrel we have found that a'ba'th kept at about 40 C. is hotenough to give a practical rate of solution. One or more of the steps ofour method above described may, if desired, be performed automaticallyor semiautomatically by machine operations and the method facilitatesmachine operations. For example, the operations A, B, C and D of Fig. 8may, if desired, be wholly automatically performed on machines either inthe exact order of steps A, B, C and D or with a different sequence. Itis deemed unnecessary to illustrate apparatus for carrying out thesemachine operations.

In the particular embodiment shown in Fig. 1, the invention isillustrated as being embodied in that type of radio tube where twoheating filament units 5, E are connected in series across ordinaryhouse voltage lines from to volts with each heating filament thereforconsuming roughly 55 to 60 volts but one of these identical unitstogether with its cathode 2 is omitted from the drawings for conveniencein illustration.

It is understood, however, that the invention is not limited to filamentstructures of any particular voltage limit and an important advantage ofour invention is that within practical limits there is no limit to thefineness of the filamentary wire that can be processed according to thisinvention to form the highly improved filamentary units of the abovedescribed structure and accordingly the invention is particularlyadapted to the production of higher voltage filaments than the 50 oddvolts of the filament mentioned above. By the structures and practicesabove described theloss in waste or discarded material is minimized andthe filament structures have the advantage above set forth.

For convenience in illustration the coils of the wire l5 are omittedfrom certain parts of the mandrel Hi as shown in Figs. 8 and 9, and alsofrom certain parts of the terminals 6 as shown in Figs. 4 and 7, and inthese and other figures of the drawings the spacing of the filamentarycoils from each other is exaggerated for convenience in illustration.

This application is a division of our co-pending application Serial No.608,960 filed August 4, 1945, now Patent No. 2,482,826, grantedSeptember 2'7, 1949.

We claim:

1. The method of making an elongated coiled non-self-supporting cathodeheating filament unit for thermionic tubes comprising the steps offlattening the ends of a unit of filament wire closely wound about amandrel and embedding the adjacent filament turns in the flattenedsurfaces of the unit, forming the unit into a V and immersing the V unitthus formed into a chemical bath to dissolve out the mandrel up topoints spaced from the flattened parts and then lower- "'7 ing; the vunit into the bath forredueing the diameter of. the inner ends of theremaining part of the mandrel. V 2. The method of making an elongatedcoiled non self-supporting cathode filament comprising the steps ofwinding filament wire on a mandrel, flattening the ends of the mandreland at least partially-embedding the filament in the mandrel. tormingthe mandrel into a V-shape and dissolving out by means of a chemicalbath the central part of the mandrel between points spaced from theembedded filament part, and subjecting the remaining mandrel ends tosaid bath by partially immersing them therein to produce a taperthereon. a I

HARRY BENDER.

B. VOORHIS.

*8 REFERENCES. CITED me of this patent:

5 UNITED STATES PATENTS v Number Name Date 2,075,910 Robinson Apr. 6,1937 2,287,460 Wagenhals et a1. June 23, 1942 2,359,302 Curtis Oct. 3,1944

